1. Field of the Invention
The invention relates to a cosmetic preparation comprising a complex of cyclodextrin and vitamin F, and to preferred complexes of cyclodextrins and vitamin F.
2. The Prior Art
Cyclodextrins are cyclic oligosaccharides which are built up from 6,7 or 8 α(1-4)-linked anhydroglucose units. The α-, β- or γ-cyclodextrins produced by enzymatic starch conversion differ in the diameter of their hydrophobic cavity and are generally suitable for the inclusion of numerous lipophilic substances.
Vitamin F consists essentially of a mixture of essential fatty acids (EFA), in particular omega-6-polyunsaturated fatty acids. Therefore, for the purposes of the present invention, vitamin F is preferably understood as meaning EFA, in particular omega-6-polyunsaturated fatty acid. The body is unable to produce EFA by itself in the required amount; however, an adequate supply is essential for natural functions of the body. The expression “essential fatty acids” used in the present application includes preferably unsaturated fatty acids with chain lengths greater than or equal to 18 carbon atoms which have at least two double bonds. The omega-6-polyunsaturated fatty acids are particularly preferably linoleic acid and its isomers, linolenic acid and its isomers, and other acids which are very sensitive to oxidation. As has been found, vitamin F develops certain properties which are particularly desirable, inter alia, for improving the appearance of the skin.
In investigations, it was in particular found that combinations of at least one essential fatty acid or mixtures thereof and in particular of vitamin F have a notable stability toward oxidation which is not found when essential fatty acids and, in particular, vitamin F are not used in the form of the active ingredient combination according to the invention.
The topical application of vitamins in cosmetics has already been proposed by a number of authors. Vitamins which have been particularly recommended which may be mentioned are vitamin A, vitamin B, vitamins B2, and B6, vitamin E, vitamin H and cyclodextrin complexes thereof, and certain suitable vitamin mixtures, such as a mixture of vitamin A, vitamin E and vitamin D3, which combination has a synergistic effect.
The vitamin which is of particular interest to the formulators of cosmetic products is vitamin F. It exerts a favorable effect on dry and rough skin, and on skin which exhibits particular symptoms of irritation. The use of vitamin F in cosmetics has always been impaired by the particularly acute problem which is essentially regarded as being the great instability of this material toward oxidation by the oxygen in the atmosphere. In particular, it has been found that very rapidly after storage or first use, decomposition products with a rancid odor form which prevent further use of cosmetic preparations based on this vitamin. Since vitamin F consists essentially of linoleic acid and its isomers and, in particular, linolenic acid and its isomers and other acids which are very sensitive toward oxidation, the corresponding alcohols or the esters, e.g. the triglycerides, of this acid have preferentially been used in cosmetics and in foodstuffs. These are more stable, although in this a case a considerable loss in activity has to be accepted. Possible ways of stabilizing the essential fatty acids are thus of extraordinary interest.
The expression “essential fatty acids” used in the present application particularly preferably includes unsaturated fatty acids which have at least two double bonds, such as:
linoleic acid or 9,12-octadecadienoic acid of the formulaCH3(CH2)4CH═CHCH2CH═CH(CH2)7COOHand stereoisomers thereof, in particular the z-9, z-12 isomers, and positional isomers thereof or conjugated linoleic acids, i.e.:9,11-octadecadienoic acid of the formulaCH3(CH2)5CH═CHCH═CH(CH2)7COOHand stereoisomers thereof;10,12 octadecadienoic acid of the formulaCH3(CH2)4CH═CHCH═CH(CH2)8COOHand stereoisomers thereof;α-linolenic acid or 9,12,15-octadecatrienoic acid of the formulaCH3(CH2CH═CH)3CH2(CH2)6COOHand stereoisomers thereof and in particular the z-9, z-12, z-15 isomer;γ-linolenic acid or 6,9,12-octadecatrienoic acid of the formulaCH3(CH2CH═CH)3(CH2)7COOHand stereoisomers thereof; andarachidonic acid or 5,8,11,14-eicosatetraenoic acid of the formulaCH3(CH2)4(CH═CHCH2)4CH2CH2COOH
Important physiological functions of vitamin F, inter alia due to the high content of linoleic acid, are the formation of arachidonic acid, a constituent of phospholipids (cell membranes) and prostaglandins (autocoids), which have an influence on the serum cholesterol level and the blood pressure. A lack of linoleic acid leads, in children, to growth disorders, increased susceptibility to infection, skin changes (eczema) and to impaired function of the capillaries. Vitamin F is used in wound healing disorders. The skincare properties which are to be found even for a low concentration make it an extremely valuable substance. In the field of cosmetics, therefore, there is great interest in the increased use of vitamin F, particularly in dermatological formulations. The topical application of vitamin F stabilizes the balance of fatty acids in the skin. A deficiency of vitamin F leads to damage specifically of the cell membranes of the skin (phospholipid structure) and also in the skin lipids (ceramide structure) to increased wrinkling and keratinization (“photoaging”) and to a loss in skin elasticity. The skin lipids with a high content of polyunsaturated fatty acids, such as linoleic acid, exhibit a relatively high packing density, which evidently strengthens the barrier function against microorganisms, and also reduced transepidermal water loss. This was proven in experiments on human and animal skin during topical application. In addition, skin lipids are synthesized from linoleic acid.
The main problem preventing more widespread use of vitamin F is its sensitivity toward oxidation, in particular under exposure to light.
An autoxidation takes place at the conjugated unsaturated hydrocarbon chain of the fatty acid molecule, leading to the formation of numerous decomposition products, to isomerizations and polymerizations. When fats become rancid, the linoleic acid, one of the essential fatty acids, can, for example, convert to an isomeric fatty acid with conjugated double bond, which no longer has vitamin character and may even increase deficiency damage. A viscous-liquid mass is formed from the originally oily, thin-liquid substance. The odor is perceived as intensively rancid. As a result of intermediately formed peroxides, the toxic potential of the formulations increases, the cosmetically and nutritional-physiologically desired effect of the intact vitamin F is reduced.
As stated above, vitamin F consists essentially of linoleic acid and isomers thereof, where, particularly preferably, the 9,12-isomer is present in an amount between about 40% and 70%, where the total content of the linoleic acid and isomers thereof forms about 80% to 90% of the material. The remainder of the material consists essentially of a mixture of other essential fatty acids.
CH 646049 describes the preparation of oxidation-resistant cosmetic preparations which comprise vitamin F or essential fatty acids by means of a vegetable oil, namely jojoba oil.
Biol. Food Chem. Aspects, Contrib. Lipid forum/Sik Symp., Meeting Date 1985, 165-70 describes the stabilization of lipids via the molecular inclusion of linoleic acid with cyclodextrins with caseine as antioxidant in dispersion.
Biochem. J. (1995) 308, 151-154 (printed in Great Britain) discloses the use of “soluble lipids” for biochemical processes by means of linoleic acid-CD complexes in aqueous solution.
Japanese patent specification 60181014A describes the preparation of bathing product additives containing vitamins, inter alia vitamin F, by means of cyclodextrins and diastase.